The PV access to distribution networks can cause the volatility and uncertainty of load to increase,which has a certain effect on the capacity planning of power transmission and distribution equipment.In this paper,on the basis of the probability analysis of both PV power and load in longitudinal moment,supply load is reduced by introducing a risk parameter.Then,energy storage is taken as a measure to shift electricity from peak periods to offpeak periods,so as to handle the probabilistic risk after reducing the supply load.On the basis of this principle,the energy storage capacity is optimized,and the balance between risk and economics as well as the risk factor corresponding to a maximum economic benefit is achieved.Case analyses show that the proposed method in this paper can bring certain economic benefits for the device capacity planning of distribution networks.